Petroleum refineries employ many different processes which convert crude oil into hundreds of products. A number of these processes produce sulfur-containing process streams which can be treated to regenerate active ingredients or to recover sulfur values from such streams. Sulfur-containing process streams are generated in hydrotreating processes and sulfuric acid-catalyzed alkylation. Hydrotreating includes hydrocracking and removal of undesirable components, such as sulfur and nitrogen, by distillation and/or hydrodesulfurization or hydrodenitrogenation.
Hydrotreating may generate sour gas streams, which contain valuable hydrocarbons and are rich in acid gas components (e.g., H2S and CO2). By “sour” gas streams it is meant herein to describe a stream which comprises an acid gas, typically H2S. The acid gas components must be removed to “sweeten” the sour gas stream so that the sweetened stream can be sold or used as fuel gas for the refinery's energy needs. The acid gas components must be further treated to comply with environmental regulations.
It is recognized that sour gas streams are not only generated in petroleum refining, but are also generated in natural gas processing and gasification of coal or petroleum coke.
Acid gas generated from refinery and other processes may be treated in either a sulfur recovery unit (SRU), which produces elemental sulfur, or spent acid recovery (SAR) plant, which produces purified sulfuric acid.
In SAR plants with conventional furnaces, acid gases may be directly fed to a spent acid decomposition furnace to serve as fuel source. If the acid gas provides insufficient energy for the amount of spent sulfuric acid to be decomposed, additional fuel, such as natural gas, refinery fuel gas, or other energy source is required. Added fuel is a cost to the plant. If there is excess acid gas relative to the amount of spent acid to be decomposed, too much heat is generated and quench water is added for temperature control. Most of this heat is not recoverable. Added quench water also increases the volume of gas treated downstream, and hence increases equipment size and cost.
Under oxidizing conditions (high temperature and excess oxygen), ammonia-containing acid gases contribute to fuel NOx formation. Thus, a conventional furnace has deficiencies that include adding quench water, wasted heat and higher NOx formation.
It is desirable to improve conventional processes for treating acid gases to improve heat recovery, minimize capital investment, minimize need for added fuel, and reduce NOx formation. The present invention meets these objectives.